1. Field of the Invention
The present invention relates to an ink jet recording apparatus which employs replaceable recording heads and also to an ink jet recording method which uses such an ink jet recording apparatus.
2. Description of the Related Art
Office automation machines such as personal computers, wordprocessors and so forth have become popular in recent years. A recording method called the ink jet recording method, which records information on a recording medium by discharging ink and depositing it on a recording medium, has been available as one of the means of outputting information input in these office automation machines. Basically, the ink jet recording method employs an ink jet head having a plurality of openings through which the ink is discharged by mechanical or thermal energy towards the recording medium to effect recording.
There is an increasing demand for using this recording method in combination with color image apparatuses such as a color image reader or a color video recorder, for the purpose of reproducing color photographs or color original images. To cope with such a demand, there has been a concentrated effort to develop color ink jet recording apparatuses which employ a plurality of inks of different colors. Such color ink jet recording apparatuses are required to have the ability to record halftone color images, as well as high quality color images.
These requirements are met only when various requisites are simultaneously satisfied, such as uniformity of diameter and directivity of all discharge openings, as well as uniformity of discharge pressure applied to all discharge openings.
Unfortunately, however, different recording heads have different patterns of fluctuation or variation of the characteristics of their discharge openings, due to restrictions posed by the present level of production technology and the complicated construction of the head. In addition, variations in ink discharging performance or characteristics inevitably occur among recording heads which utilize thermal energy, because of slight differences in the electrical resistance of heat-generating resistors incorporated in these recording heads.
These variations are intensified by each other so as to produce substantial differences among different recording heads, such as difference in the ink discharge rate, differences in the ink jetting direction and so forth, not to mention differences in the ink discharge rate among discharge openings within individual recording heads. Such variations in the ink discharge characteristics cause unevenness of recording density, which is critical particularly in the recording of halftone color images, and fail to meet the demand for high quality image recordings.
In order to overcome this problem, a method has been proposed in which the patterns of density unevenness exhibited by individual ink jet recording heads are obtained by measurement when the heads are produced, and correction data for correcting parameters such as head driving conditions and image processing conditions are determined and stored in a semiconductor memory such as a ROM (read only memory) mounted on each recording head. In operation, each recording head discharges ink in accordance with the parameters corrected in accordance with the correction data, whereby the variation in density unevenness among different recording heads is suppressed or substantially eliminated.
Meanwhile, a recording head cartridge has been proposed with a recording head portion and an ink tank portion integrated with the recording head portion and which is replaceably used on recording apparatuses in order to simultaneously reduce the cost of the apparatus and increase the recording quality. When a recording head is constructed in the form of a recording head cartridge of the type described, it is necessary to match the recording apparatus and the cartridge in advance of using the cartridge. Such a matching, however, cannot be obtained prior to the use of the cartridge. It has therefore been proposed to provide each head cartridge with a semiconductor memory of the type mentioned before, i.e., a semiconductor memory which stores head characteristics peculiar to each recording head.
The recording characteristics of the replaceable recording head in the form of a head cartridge integrated with an ink tank tends to change or deteriorate due to impact or changes in environmental condition which may be incurred during transport. When a new recording head is mounted on a recording apparatus, therefore, it is necessary to effect a discharge recovery operation for the purpose of recovering the original discharge performance of the recording head before the head is actually operated.
In general, a color recording apparatus simultaneously mounts a plurality of recording heads of different colors, such as cyan, yellow, magenta and black. Replaceable recording heads, therefore, should have or be associated with suitable means for preventing erroneous mounting.
Known ink jet recording apparatuses require that a discharge recovery operation be manually triggered each time a new recording head is mounted. Thus, users are inconveniently obliged to conduct, in addition to the replacement of the recording head, an operation for manually triggering the discharge recovery operation. Recording under optimum conditions cannot be performed if the user has happened to forget triggering the discharge recovery operation. Furthermore, when the recording head is of the type which has a memory storing the aforesaid correction data, the user also is required to conduct an operation for enabling the recording apparatus to read the data in the memory.
Thus, various manual functions have to be performed by the user each time a recording head is replaced, in order to obtain the optimum recording condition.